The present invention provides new liquid crystal compounds. In particular, the present invention provides liquid crystal compounds to be blended in a ferroelectric liquid crystal compound or composition to improve the properties thereof. The compounds of the present invention are usable in display elements or display devices, utilizing the electro-optical effects of the liquid crystal compounds.
(S)-2-Methylbutyl p-(p-n-decyloxybenzylideneamino)-cinnamate (DOBAMBC) is known as a ferroelectric liquid crystal compound. This Schiff base compound has been studied as a ferroelectric liquid crystal and various compounds have been prepared as the result. Known examples of these compounds are those of the general formula: ##STR4## wherein X represents H, Cl or CN, Y represents Cl or C.sub.2 H.sub.5 and * represents an asymmetric carbon atom.
However, the use of these compounds is limited, since the temperature at which they are in chiral smectic phase is higher than the room temperature and the chemical stability of them is low because they contain a Schiff base. Compounds of the structural formula: ##STR5## were proposed as compounds free of the above-described defects and attracted public attention.
Further, Zaschke Horst Stolle and Reinhard described various compounds of the formula: ##STR6## wherein m represents a number of 1 to 11 and n represents a number of 5 to 8, in Z. Chem. 1975, 15 (11), 441 to 3. U.S. Pat. No. 4,389,329 discloses compounds having a ##STR7## structure. However, neither ferroelectric chiral smectic liquid crystal compounds are disclosed therein nor a suggestion of them is given therein.